KR20200120902A - Twin screw mixer-extruder with presser body to define the controlled volume of the mixing chamber - Google Patents

Abstract

A device for mixing and extruding plastic materials, e.g. rubber-based and silicone-based materials, a dump equipped with two conical screws (2) converging towards an extrusion die (3) suitable for closing by means of a closing means (4) Comprising an extruder body, the conical screw 2 is accommodated inside the low pressure mixing chamber 1 and inside a pair of converging conical channels defining the high pressure chamber 2', and the low pressure chamber 1 is in the extrusion direction. A frame defining a movable wall suitable for causing a controlled volume change of each chamber 1, 2'in the high pressure chamber 2'and/or the low pressure chamber 1 A device that accommodates the main body (5, 5', 6).

Description

Twin screw mixer-extruder with presser body to define the controlled volume of the mixing chamber

The present invention relates to a mixer-extruder for rubber, silicone, plastic and thermoplastic materials, or other materials, and more particularly to a mixer-extruder provided with means for temporarily adjusting the compounding chamber.

In some types of screw extruders for synthetic materials, in particular rubber, elastomer, plastic and/or thermoplastic plastic materials, or materials with good elasticity such as silicone, the feed to the extrusion screw is a loading hopper ( It is well known that this is done through loaidng hopper).

Commercially available extruders that have proven to be particularly effective are those described in WO2005/039847 in the name of the same applicant, which is incorporated herein by reference, wherein a compounding function is provided in an extruder of the twin screw dump extruder type.

More precisely, referring to FIG. 1, which shows this prior art machine in partial cross-section, the compounding chamber 1 is directed towards the extrusion die 3 which can be closed by a blind flange or a closing cover 4. It houses a pair of extruded conical screws (2) that push the The blending chamber 1 is provided with an inlet 1a that is open to a feed hopper (not shown). The closing cover 4 closes the extrusion die 3 and recirculates the material to the compounding chamber 1 to be compounded by two conical screws. The material is actually driven forward by a pair of counter rotating screws, i.e. towards the extrusion die 3, which is then brought back when the die is closed by the cover 4. In certain applications, the rotation of the two screws may be temporarily reversed to improve the compounding effect.

The cover 4 can be opened or easily removed so that the extrusion die 3 remains closed during the compounding step until desired, and then remains open to allow the extruded material to flow out when mixing is complete.

When the extrusion die 3 of the dump extruder is closed by the cover, the material introduced by the hopper is homogeneously blended by recirculating itself inside the chamber 1.

Particularly during operation, by means of a blind flange 4 arranged in the closed position, the load to be compounded, for example a formulation already premixed in another machine, or a bulk component such as rubber, fillers, accelerators, is transferred to the feed hopper. While being loaded and fed to the mixing chamber 1, the motor pushes the material to be compounded into the die while rotating the conical screw in the reverse direction. However, the closed cover 4 does not allow the mixture to flow out of the chamber and the mixture is recycled back to the chamber. Thus, an increasing pressure gradient is determined between the low pressure material supply region and the high pressure "ducted" region near the blind flange 4. Recirculation between the zones with variable pressures of the various basic components enables quick and effective blending of the mixture.

The two counter-rotating conical screws are partially accommodated inside the large chamber 1 in which the material is loaded, and partially inside the converging and intersecting conical channels, and the peripheral profile of the screw threads is at the channel surface. It extends adjacently. Thus, the material is forced into an increasingly narrow volume following the vane profile of the screw, increasing the pressure. In order to achieve recirculation of the material in at least the foremost region of the conical channel (when the cover 4 is closed), the circumferential wall is provided with an extension such that the screw vanes are spaced a distance from the wall. Typically, an enlarged portion is provided on top of the receiving channel. Due to the presence of this extension of the channel for receiving the extrusion screw, when the cover is closed, the material is circulated back and returned to the low pressure region of the chamber 1, resulting in an effective blending.

This extruder is completely functional, but the applicant has indicated that there is room for improvement. In fact, the material to be blended is freely disposed within the mixing chamber 1 based on the local pressure, which may cause the mixing to be stagnant or delayed, and sometimes the temperature and pressure of the material may rise excessively. Noted. Therefore, it would be desirable to better tune the process during the compounding step.

In the prior art, some single configurations of the extruder have already been proposed, but here a movable element is used at least to control the input of material into the extruder screw. For example, DE102007033355 discloses an extruder provided with a material thrusting plate operating at the inlet hopper of the extruder. In contrast, US2016/0361697 relates to a mixer provided with a removable closing element that opens and closes the material mixing chamber. However, none of these prior art systems are capable of being adapted to both the compounding conditions and the extrusion conditions as they cannot control the pressure and temperature conditions of the material to be compounded during the process.

Therefore, the fundamental problem of the invention is to overcome the above-described drawbacks and supply the extruder and compounder of the rubber-based or silicone-based material as described above, which enables better control over the mixing and temperature/pressure of materials as well as the mixing time during the process. Is to do.

This object is achieved through the features defined in essential terms in the appended claims.

In particular, according to the first embodiment, an apparatus for mixing and extruding plastic materials, for example rubber-based and silicone-based materials, is provided and equipped with two conical screws converging towards an extrusion die suitable to be closed by a closing means. A dump extruder body, wherein the conical screw is received in the low pressure mixing chamber and in a pair of converging conical channels defining the high pressure chamber, the low pressure chamber corresponding to a region upstream with respect to the extrusion direction, the high pressure chamber and/or Or the low pressure chamber is provided with a presser body defining a movable wall suitable for causing a controlled volume change of each chamber.

According to a preferred embodiment, at least the high-pressure chamber is provided with a presser body whose position is controlled.

According to another embodiment, the presser body of the low pressure chamber is arranged to close the plastic material loading opening, such as the inlet hopper of the dump extruder.

In general, the presser body is mounted to be slidably movable, but may be mounted to have more than one angle of rotation. The presser body is preferably movable between a raised (or grooved) position and a lowered (or actuated) position under the action of a controlled actuator. According to a variant, the actuator determines the constant position of the presser during mixing.

According to a preferred embodiment, the presser body has a movable wall formed of two intersecting conical portions to fit and follow the profile of the vanes of the two screws.

It is understood that the presser body is displaced at least during the compounding step and the closing means prevents the plastic material from passing through the extrusion die.

Further, the closing means may be in the form of a withdrawal gear pump that is stopped and closes the outlet of the die.

Further features and advantages of the present invention are presented by way of non-limiting example only, and will become more apparent from the following detailed description of some preferred embodiments shown in the accompanying drawings.
1 is a cross-sectional side view of a prior art extruder/mixer system as already mentioned.
2A is a schematic enlarged view of the details of the single compounding chamber of FIG. 1, but relates to an extruder system according to a first embodiment of the present invention.
Fig. 2B is a view similar to that of Fig. 2A, but relates to a variation of the first embodiment.
Fig. 3A is a view similar to that of Fig. 2A, but relates to a second preferred embodiment of the present invention.
3B is a cross-sectional view taken along line III-III of FIG. 3A.
Fig. 4A is a view similar to Fig. 3A in the step of expanding the recirculation chamber.
4B is a cross-sectional view taken along line IV-IV of FIG. 4A.
Fig. 5 is a view similar to that of Fig. 2A, but relates to a third embodiment.

The extruder and mixer are shown in Fig. 1 and consist of the basic elements already described in the introductory part with reference to the document WO2005/039847, incorporated herein by reference.

In particular, the "dump extruder" has a machine body defining a compounding chamber 1 containing a pair of axially arranged conical extrusion screws 2 and a cross helical vane spiral converging towards the extrusion die 3.

The extrusion die 3 can be closed by suitable closing means 4 (shown schematically in the drawings), such as a removable cover, or simply by a pull-out gear pump which is stopped and closes the outlet of the die.

The compounding chamber 1 has an upper inlet 1a into which a material such as a rubber-based or silicone-based material to be treated is introduced.

In the front part of the chamber 1, in the vicinity of the extrusion die 3, a pair of conical screws 2 are received in a converging conical channel with an inner wall almost contacting the vane edges of the conical screws. Thus, the cross-sectional profile of this conical channel is formed by two intersecting circles. In at least one region of this cross-sectional profile, the inner wall of the channel is separated from the vanes of the conical screw 2 by having an extension and defines a material recycling chamber. In general, this extension is provided on top of the conical screw 2 (see area 2'in Fig. 4B).

Next, referring to Figs. 2A and 2B, according to the first embodiment of the present invention, in the inlet 1a of the mixing chamber 1, a closing body 5 mounted to lift and lower, referred to as a presser hereinafter, is provided. It should be noted that it becomes.

In particular, according to the first variant, the presser 5 is linearly slidably mounted between the raised position and the position in contact with the material inside the chamber 1 (as shown in Fig. 2A), and in this case the presser 5 (5) is made essentially like a piston, which closes the inlet (1a) and can move substantially therein along an axis substantially perpendicular to the transverse plane of the pair of screws (2). It becomes an element to variably close

According to the second variant, the presser 5'is mounted by pivoting about the hinge 5a between the upwardly rotated position and the downwardly rotated position (as in Fig. 2B), and Contact.

Since the presser (5 or 5') is mounted with a certain clearance to the inlet (1a), it is not necessary to seal the entrance to the chamber (1), and it is placed on the material blended inside the chamber in the low pressure region of the chamber (1) This is to apply local pressure to the material itself. That is, the presser 5 or 5'is for reducing the volume of the chamber 1 in a controlled manner so that the pressure and temperature of the material can be adjusted as desired in a controlled manner.

The localized pressure action by the presser 5 exerts an advantageous effect on the material compounded by a pair of conical screws. In particular, the material returning from the high pressure region to the low pressure region is held inside the vane of the conical screw by the presser to improve the mixing effect.

The pressure in this low pressure region of the chamber 1 allows better control of the amount of reflux of the material to promote and accelerate the homogenizing effect of the material.

To this end, the presser is simply manufactured in the form of a heavy body mounted movably as shown above in such a way that the same pressure (due to its own weight affected by gravity) is always applied to the material, or hydraulic or electric Alternatively, it may be manufactured in the form of a piston that is movable under the action of a controlled actuator (not shown) such as a pneumatic jack.

In the second case, the actuator can be controlled to produce a weight-like effect by applying a constant force, or to actually set a desired volume in which the pressure can change periodically by holding the piston in a fixed position. Further, the position and pressing force of the pressers 5 and 5'can be changed and set during the compounding and extrusion cycle.

The presser 5 need not necessarily have a circular cross-sectional shape, but can take any other shape, for example a square, rectangular, triangular or circular cross-sectional shape. Obviously. It is only necessary to have a shape that fits the outline of the inlet 1a.

In two variants of the first embodiment of Figs. 2A and 2B, the pressers 5, 5'are applied in the so-called low pressure region of the chamber 1, ie the region immediately next to the loading inlet 1a.

In contrast to this, in the preferred embodiment (Figs. 3A to 4B), the presser 6 operates in the high pressure region of the extrusion chamber 1, ie in the region where two conical screws are received in each conical channel. In the high-pressure chamber, the pressure is usually in the range of 5 to 200 bar. In this case, the inlet 1a of the hopper can be opened and closed by a simple cover defining a constant volume, and pressure control for the compounded material is exerted only by the presser 6.

In particular, as well shown by the comparison of FIGS. 3B and 4B, in this preferred embodiment the presser 6 constitutes a movable wall of the extension of the conical channel defining the high pressure mixing chamber 2'. . Thus, it is possible to control the volume change of the high pressure mixing chamber 2'by displacing the presser 6, so that the pressure change and indirectly the temperature change of the material to be processed can be determined.

In this case, since the presser 6 operates in a high pressure region where the wall of the conical channel is adjacent to the vane edge of the screw, the presser 6 defines a movable wall formed by two intersecting conical portions , Which in fact constitutes part of each conical channel (as clearly seen in Figure 4B).

Since the size of the high pressure region is much smaller than that of the low pressure region, it is certainly desirable that the presser 6 is controlled by an actuator capable of exerting a sufficient total pressure on the material while acting on the smaller presser. In addition, this area, i.e. the volume change of the high-pressure mixing chamber, has proven to be very effective because it causes a high proportion of change and thus has a significant effect on the behavior of the material.

According to the third embodiment, both pressers 5 and 5'are provided in the low pressure region and the controlled presser 6 is provided in the high pressure region. The control action is preferably performed for both pressers to have maximum intervention flexibility.

As can be appreciated, by using a mobile presser (5, 5') and/or presser (6) that changes the volume of the high pressure chamber 2'and/or the low pressure chamber 1, the degree of mixing and It is possible to add control elements that allow optimal control of the process speed/performance.

It has also been found that it is convenient to control the intervention of the presser during the extrusion step, ie when the closing cover 4 is opened and the material is extruded through the die 3. Thus, at this stage, it is possible to better control the material outlet pressure and improve the emptying of the mixing chamber, avoiding the inclusion of air in the material if necessary.

However, the present invention should not be considered to be limited to the specific arrangements shown above showing only some exemplary implementations thereof, but without departing from the scope of the present invention itself as defined by the following claims. It is understood that all different variations are possible within the authority.

Claims (9)

As an apparatus for mixing and extruding plastic materials, such as rubber-based and silicone-based materials,
It comprises a dump extruder body equipped with two conical screws (2) converging towards an extrusion die (3) suitable for closing by means of a closing means (4), the conical screw (2) being inside the low pressure mixing chamber (1) , And a pair of converging conical channels defining a high-pressure chamber 2', and the low-pressure chamber 1 corresponds to a region upstream with respect to the extrusion direction,
In the high pressure chamber 2 ′ and/or the low pressure chamber 1 a presser body 5, 5 ′ forming a movable wall suitable for defining the controlled volume change of each chamber 1, 2 ′. ) Is provided. The method of claim 1,
At least the high-pressure chamber (2') is provided with a presser body (6) whose position is controlled. The method of claim 1,
The presser body (5, 5') of the low pressure chamber (1) is arranged to close the plastic material loading opening (1a). The method according to any one of claims 1 to 3,
The presser body (5, 6) is a device mounted to be slidably movable. The method according to any one of claims 1 to 4,
The presser body (5, 6) is a device that is movable between a raised position and a lowered position under the action of a controlled actuator. The method of claim 5,
The actuator is a device for determining a constant position of the presser (5, 6). The method according to any one of claims 1 to 6,
The presser (6) has a movable wall formed by two intersecting conical sections. The method according to any one of claims 1 to 7,
The presser (5, 5', 6) is displaced at least during the compounding step, and the closing means (4) prevents plastic material from passing through the extrusion die (3). The method of claim 8,
A device in the form of a withdrawal gear pump in which the closing means (4) is stopped and closes the outlet of the die (3).

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